Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/002—Heat treatment of ferrous alloys containing Cr
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals

Definitions

• This application is directed to ferritic stainless steel that hardly has deterioration in corrosion resistance due to carbon and nitrogen, which enter a weld bead from an opposite material to be welded, or due to nitrogen, which enters a weld bead from atmospheric air when welding is performed.
• ferritic stainless steel In the case of ferritic stainless steel, satisfactory corrosion resistance can be achieved with smaller Ni content than in the case of austenite stainless steel. Since Ni is an expensive element, it is possible to manufacture ferritic stainless steel at lower cost than austenite stainless steel. In addition, ferritic stainless steel has some characteristics superior to those of austenite stainless steel, for example, higher thermal conductivity, lower thermal expansion coefficient, and excellent stress corrosion cracking resistance. Therefore, ferritic stainless steel has been widely used for automobile exhaust system members, architectural materials such as roofs and fittings, and materials for plumbing products such as kitchen appliances, water storage tanks and hot water storage tanks.
• austenite stainless steel in particular, for example, SUS304 (18% Cr-8% Ni) (JIS G 4305) and ferritic stainless steel are used in combination in many cases.
• TIG welding is generally used as a method for welding such kinds of stainless steel.
• a weld zone is required to have corrosion resistance as high as that of a base material zone.
• Patent Literature 1 discloses ferritic stainless steel having improved intergranular corrosion resistance by adding Ti and Nb in combination.
• Patent Literature 2 discloses steel having improved intergranular corrosion resistance by adding Nb.
• an object of the present disclosure is to provide ferritic stainless steel excellent in terms of the corrosion resistance of a weld zone which does not require excessive amounts of Ti or Nb to be added.
• the present inventors diligently conducted investigations regarding techniques with which it is possible to inhibit a deterioration in the corrosion resistance of a weld zone better than ever.
• the present inventors conducted systematic investigations regarding acceptable degree of sensitization with which it is possible to achieve sufficient corrosion resistance for a weld zone using steel containing Cr in an amount of 16 to 20 mass %, and as a result, found that a deterioration in the corrosion resistance of a weld zone due to sensitization becomes noticeable in the case where a grain boundary coverage factor of a ferrite phase by Cr carbonitrides (refer to a measurement method for determining a grain boundary coverage factor in the EXAMPLE) is more than 40%.
• the present inventors conducted investigations regarding a method for decreasing the grain boundary coverage factor of a ferrite phase by Cr carbonitrides, and as a result, found that, in order to improve the corrosion resistance of a weld zone, it is very effective to stabilize an austenite phase by adding Mn and Cu, which are austenite-forming elements.
• atomic symbols in the relational expression respectively represent the contents (mass %) of the corresponding elements.
• Ferritic stainless steel having excellent corrosion resistance of a weld zone, the steel having a chemical composition containing, by mass %, C: 0.001% or more and 0.025% or less, Si: 0.05% or more and 0.30% or less, Mn: 0.35% or more and 2.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 0.05% or more and 0.80% or less, N: 0.001% or more and 0.025% or less, Cr: 16.0% or more and 20.0% or less, Ti: 0.12% or more and 0.50% or less, Nb: 0.002% or more and 0.050% or less, Cu: 0.30% or more and 0.80% or less, Ni: 0.05% or more and less than 0.50%, V: 0.01% or more and 0.50% or less, and the balance being Fe and inevitable impurities, in which relational expression (1) below is satisfied:
• ferritic stainless steel having excellent corrosion resistance of a weld zone even under the welding conditions which C and N enter a base material from an opposite material to be welded.
• C is an element which is inevitably contained.
• the C content is set to be 0.001% or more and 0.025% or less.
• the C content be as small as possible from the viewpoint of corrosion resistance and workability, it is not preferable from the viewpoint of productivity that C content be extremely decreased, because there is an increase in the time taken for refining. Therefore, it is preferable that the C content be 0.003% or more and 0.018% or less, or more preferably 0.005% or more and 0.012% or less.
• Si 0.05% or More and 0.30% or Less
• Si is an element which is effective for improving the corrosion resistance of a weld zone. It is necessary that the Si content be 0.05% or more in order to realize such an effect, and, the larger the Si content, the larger the effect. However, it is not desirable that the Si content be more than 0.30%, because there is a deterioration in the formability and toughness of a weld zone. Therefore, the Si content is set to be 0.05% or more and 0.30% or less, preferably 0.05% or more and 0.25% or less, or more preferably 0.08% or more and 0.20% or less.
• Mn is a particularly important element in the present disclosure.
• Mn is an element which is effective as a deoxidizing agent and which is effective for stabilizing an austenite phase.
• the Mn content is set to be 0.35% or more and 2.0% or less, preferably 0.50% or more and 1.5% or less, or more preferably 0.75% or more and 1.25% or less.
• the P content is an element which is inevitably contained in steel and, in the case where the P content is excessively large, there is a deterioration in weldability and intergranular corrosion tends to occur. These tendencies become noticeable in the case where the P content is more than 0.05%. Therefore, the P content is set to be 0.05% or less, or preferably 0.03% or less.
• the S content is set to be 0.01% or less, or preferably 0.008% or less.
• Al is, like Si, an element which improves the corrosion resistance of a weld zone. Since Al has higher affinity for N than Cr has, N is precipitated in the form of Al nitrides instead of Cr nitrides in the case where N is mixed into a weld zone, which results in the effect of inhibiting sensitization.
• Al is a chemical element which is also effective for deoxidization in a steel-making process. Such effects are realized in the case where the Al content is 0.05% or more. However, in the case where the Al content is more than 0.80%, since there is coarsening of the ferrite crystal grain, there is a deterioration in workability and manufacturability. Therefore, the Al content is set to be 0.05% or more and 0.80% or less, preferably 0.10% or more and 0.60% or less, or more preferably 0.15% or more and 0.50% or less.
• N is, like C, an element which is inevitably contained in steel. There is an increase in strength in the case where the N content is large, and there is an improvement in workability as the N content becomes small. It is appropriate that the N content be 0.001% or more in order to achieve sufficient strength. However, it is not desirable that the N content be more than 0.025%, because there is a significant deterioration in ductility, and because there is a deterioration in corrosion resistance due to promoting the precipitation of Cr nitrides. Therefore, the N content is set to be 0.001% or more and 0.025% or less. It is preferable that the N content be as small as possible from the viewpoint of corrosion resistance.
• the N content be 0.003% or more and 0.025% or less, more preferably 0.003% or more and 0.015% or less, or even more preferably 0.003% or more and 0.010% or less.
• the Cr content is an element which is the most important for achieving the corrosion resistance for stainless steel. It is not desirable that the Cr content be less than 16.0%, because it is not possible to achieve sufficient corrosion resistance in a weld bead and in the vicinity of the weld bead, in which there is a decrease in the amount of Cr in a surface layer due to oxidation as a result of performing welding, and because sensitization, which is caused by N which is mixed in from an opposite material to be welded or from atmospheric air when welding is performed, is promoted to a higher degree. On the other hand, it is not desirable that the Cr content be more than 20.0%, because there is a deterioration in toughness, and because there is a deterioration in descaling performance after annealing. Therefore, the Cr content is set to be 16.0% or more and 20.0% or less, preferably 16.5% or more and 19.0% or less, or more preferably 17.0% or more and 18.5% or less.
• Ti is an element which is effective for inhibiting a deterioration in corrosion resistance due to sensitization due to the precipitation of Cr carbonitrides as a result of being more readily to combine with C and N than other elements are. Such an effect is realized in the case where the Ti content is 0.12% or more. However, it is not desirable that the Ti content be more than 0.50%, because surface defects occur due to the formation of coarse Ti carbonitrides. Therefore, the Ti content is set to be 0.12% or more and 0.50% or less, preferably 0.15% or more and 0.40% or less, or more preferably 0.20% or more and 0.35% or less.
• Nb 0.002% or More and 0.050% or Less
• Nb is an element which is effective for inhibiting a deterioration in corrosion resistance due to sensitization due to the precipitation of Cr carbonitrides as a result of being more readily to combine with C and N than other elements are.
• Nb is effective for improving the toughness and bendability of a weld zone as a result of refining the crystal grain in a weld zone. Such effects are realized in the case where the Nb content is 0.002% or more.
• the Nb content is set to be 0.002% or more and 0.050% or less, preferably 0.010% or more and 0.045% or less, or more preferably 0.015% or more and 0.040% or less.
• Cu is an element which improves corrosion resistance and which is effective particularly for improving the corrosion resistance of a base material and a weld zone which are placed in an aqueous solution or to which slightly acidic water drops adhere.
• Cu is, like Ni, a strong austenite-forming element
• Cu is effective for inhibiting sensitization due to the precipitation of Cr carbonitrides as a result of inhibiting the formation of a ferrite phase in a weld zone.
• the Cu content is set to be 0.30% or more and 0.80% or less, preferably 0.30% or more and 0.60% or less, or more preferably 0.35% or more and 0.50% or less.
• Ni 0.05% or More and Less than 0.50%
• Ni is an element which improves the corrosion resistance of stainless steel and which inhibits the progress of corrosion in a corrosive environment in which active dissolution occurs because a passivation film cannot be formed.
• Ni is a strong austenite-forming element
• Ni is effective for inhibiting sensitization due to the precipitation of Cr carbonitrides as a result of inhibiting the formation of a ferrite in a weld zone.
• Such effects are realized in the case where the Ni content is 0.05% or more.
• the Ni content is set to be 0.05% or less and less than 0.50%, preferably 0.10% or more and 0.30% or less, or more preferably 0.15% or more and 0.25% or less.
• V 0.01% or More and 0.50% or Less
• V is an element which improves corrosion resistance and workability and which is effective for deteriorating the degree of the sensitization of a weld zone by inhibiting the formation of Cr nitrides as a result of combining with N when N is mixed into a weld zone.
• the V content is 0.01% or more.
• the V content is set to be 0.01% or more and 0.50% or less, preferably 0.05% or more and 0.30% or less, or more preferably 0.08% or more and 0.20% or less.
• atomic symbols in the relational expression respectively represent the contents (mass %) of the corresponding elements.
• the right-hand side value of relational expression (1) is set to be more than 0.5, preferably 0.60 or more, or more preferably 0.70 or more.
• the chemical composition described above is the basic chemical composition of the disclosed embodiments, and the balance of the chemical composition consists of Fe and inevitable impurities.
• the inevitable impurities Ca: 0.0020% or less is acceptable.
• the elements below may be added to meet objectives such as inhibition of the sensitization of a weld bead and improvement of the corrosion resistance.
• Zr is effective for inhibiting sensitization by combining with C and N. Such an effect is realized in the case where the Zr content is 0.01% or more. However, in the case where the Zr content is more than 0.50%, there is a deterioration in workability. An excessive Zr content is not preferable also because there is an increase in manufacturing costs since Zr is an expensive element. Therefore, in the case where Zr in added, it is preferable that the Zr content be 0.01% or more and 0.50% or less, or more preferably 0.10% or more and 0.35% or less.
• W is, like Mo, effective for improving corrosion resistance. Such an effect is realized in the case where the W content is 0.01% or more. However, it is not preferable that the W content be more than 0.20%, because there is a deterioration in manufacturability due to, for example, an increase in rolling load since there is an increase in strength. Therefore, in the case where W is added, it is preferable that the W content be 0.01% or more and 0.20% or less, or more preferably 0.05% or more and 0.15% or less.
• REM Since REM is effective for improving oxidation resistance, REM is effective for inhibiting the formation of a Cr depletion zone immediately behind welding temper color by inhibiting the formation of oxidized scale. In order to realize such an effect, it is necessary that REM content be 0.001% or more. However, in the case where REM content is more than 0.10%, there is a deterioration in manufacturability such as pickling performance. Excessive REM content is not preferable also because there is an increase in manufacturing costs since REM is, like Zr, an expensive element. Therefore, in the case where REM is added, it is preferable that the REM content be 0.001% or more and 0.10% or less, or more preferably 0.010% or more and 0.08% or less.
• Co is an element which improves toughness. Such an effect is realized in the case where the Co content is 0.01% or more. On the other hand, in the case where the Co content is more than 0.20%, there is a deterioration in manufacturability. Therefore, in the case where Co is added, it is preferable that the Co content be 0.01% or more and 0.20% or less, or more preferably 0.05% or more and 0.15% or less.
• B is an element which improves secondary working embrittlement, and such an effect is realized in the case where the B content is 0.0002% or more.
• the B content is more than 0.010%, a deterioration in ductility may be caused due to excessive solid solution hardening. Therefore, in the case where B is added, it is preferable that the B content be 0.0002% or more and 0.010% or less, or more preferably 0.0010% or more and 0.0075% or less.
• Sb is, like Al, an element which is effective for capturing N which is mixed in from atmospheric air when a gas shield is insufficiently effective when TIG welding is performed
• Sb is an element which is effective particularly in the case where stainless steel is used for a structure having a complex shape for which it is difficult to provide a sufficient gas shield.
• the Sb content is 0.05% or more.
• the Sb content is more than 0.30%, there is a deterioration in surface quality due to the formation of nonmetallic inclusions in a steel-making process, and there is a deterioration in the toughness of a hot-rolled steel sheet. Therefore, in the case where Sb is added, it is preferable that the Sb content be 0.05% or more and 0.30% or less, or more preferably 0.05% or more and 0.15% or less.
• Molten steel having the chemical composition described above is prepared by using a known method such as one using a converter, an electric furnace, or a vacuum melting furnace, and a steel material (slab) is manufactured by using a method such as a continuous casting method or an ingot casting-slabbing method.
• This slab is made into a hot-rolled steel sheet by performing hot rolling after heating the slab at a temperature of 1100° C. to 1250° C. for 1 to 24 hours or by performing hot rolling directly on the slab as cast without heating.
• the hot-rolled steel sheet is subjected to hot-rolled steel sheet annealing at a temperature of 800° C. to 1100° C. for 1 to 10 minutes.
• hot-rolled steel sheet annealing may be omitted for some purposes of use.
• a cold-rolled steel sheet is manufactured by performing cold rolling, and a product is completed by performing recrystallization annealing and pickling.
• cold rolling be performed with a rolling reduction of 50% or more from the viewpoint of elongation, bendability, press formability, and shape. It is generally preferable that the recrystallization annealing of a cold-rolled steel sheet be performed at a temperature of 800° C. to 950° C. from the viewpoint of obtaining satisfactory mechanical properties and pickling performance in the case of a product having a surface finishing No. 2B in accordance with JIS G 0203.
• it is effective to perform BA annealing (bright annealing) as a finishing process on a member which is used for a part where luster is required.
• polishing may be performed after cold rolling has been performed and after forming has been performed in order to improve surface quality.
• Stainless steels having the chemical compositions given in Table 1 were prepared by using a small-size vacuum melting furnace having a capacity of 50 kg. These ingots were heated at a temperature of 1150° C. for 1 hour and then made into hot-rolled steel sheets having a thickness of 3.5 mm by performing hot rolling. Subsequently, these hot-rolled steel sheets were subjected to hot rolled steel sheet annealing at a temperature of 950° C. for one minute, then subjected to shot blasting of surface, and then subjected to descaling by performing pickling in which the hot-rolled steel sheets were dipped in a 20% mass %-sulfuric acid solution having a temperature of 80° C. for 120 seconds and then dipped in a mixed acid containing 15 mass % of nitric acid and 3 mass % of fluoric acid and having a temperature of 55° C. for 60 seconds.
• the resultant steel sheets were cold-rolled to a thickness of 0.8 mm and subjected to recrystallization annealing in a slightly reducing atmosphere (hydrogen: 5 vol %, nitrogen: 95 vol %, and dew-point: ⁇ 40° C.) at a temperature of 900° C. for one minute in order to obtain cold-rolled and annealed steel sheets.
• the cold-rolled and annealed steel sheets were subjected to a descaling treatment by performing electrolytic pickling in mixed acid containing 15 mass % of nitric acid and 0.5 mass % of hydrochloric acid and having a temperature of 50° C. in order to obtain cold-rolled, pickled, and annealed steel sheets.
• Table 1-1 and Table 1-2 continued make one table as a whole.
• Butt TIG welding was performed on the obtained cold-rolled steel sheet and a commercially available cold-rolled steel sheet having a thickness of 0.8 mm of austenite stainless steel, that is, SUS304 (C: 0.07 mass %, N: 0.05 mass %, Cr: 18.2 mass %, and Ni: 8.2 mass %) (cold-rolled steel sheet according to the present disclosure: base material and welding opposite material: SUS304).
• Welding current was 90 A, welding speed was 60 cm/min, and Ar gas containing 8 vol % of nitrogen and 2 vol % of oxygen was used as a shielding gas at a flow rate of 15 L/min.
• the width of the obtained weld bead at a front side was about 3 mm.
• Test pieces including the obtained weld beads were taken in order to perform tests below.
• Test pieces of 20 mm square were taken from the cold-rolled and annealed test piece and the welded sample piece, and the sample pieces were covered with seal materials with measuring surfaces of 10 mm square being left uncovered.
• the test piece was taken such that the weld bead was included, and welding temper color (oxide film) was left as it was.
• Pitting potentials of the base material and weld zone of each of these test pieces were determined in a 3.5 mass %-NaCl solution having a temperature of 30° C. At this time, although polishing of a test piece or a passivation treatment was not performed, measuring methods other than those were in accordance with JIS G 0577 (2005).
• a test piece of 100 mm square was taken from the welded sample piece such that the weld bead was included in the test piece, the surface of the test piece was subjected to polish finishing with a #600 emery paper, the end faces of the test piece were sealed, and then the test piece was subjected to a cyclic neutral salt spray test in accordance with JIS H 8502.
• One cycle of a cyclic neutral salt spray test includes spraying 5 mass %-NaCl solution (35° C., 2 hours)->drying (60° C., 4 hours, relative humidity: 20% to 30%)->moistness (40° C., 2 hours, relative humidity: 95% or more). After performing this cycle 15 times, a case where corrosion did not occur in a base material and a weld zone was judged as satisfactory.
• a test piece for the observation of metallographic microstructure was taken in a direction at a right angle to the weld bead direction of the welded sample piece, the test piece was subjected to mirror polishing and etching using picric acid-hydrochloric acid solution in order to expose metallographic structure and precipitations, and the observation of microstructure and the phase identification of precipitations were performed by using a scanning electron microscope and energy dispersive X-ray spectrometry in order to determine the grain boundary coverage factor of a ferrite phase by Cr carbonitrides in a weld bead.
• a JIS 13B tensile test piece was taken from the obtained cold-rolled and annealed steel sheet in the direction parallel to the rolling direction, and a tensile test was performed in accordance with JIS Z 2241 in order to determine breaking elongation.
• the pitting potential of a base material was 150 my or more
• the pitting potential of a weld bead was 0 mV or more
• corrosion did not occur in a cyclic neutral salt spray test, and hence sufficient corrosion resistance was achieved even when welding with austenite stainless steel was performed.
• the grain boundary coverage factor of a ferrite phase by Cr carbonitrides after welding was 40% or less, and the specified effect of preventing sensitization was realized.
• breaking elongation in a tensile test was 25% or more, which means satisfactory workability was achieved, and further surface defects were not observed.
• Ferritic stainless steel according to the present disclosure can suitably be used in applications, in which structures are manufactured by performing welding, for example, materials for automobile exhaust system such as mufflers and architectural materials such as fittings, air vents, and ducts.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=52431298

Family Applications (1)

Country Status (7)

Cited By (1)

Families Citing this family (2)

Family Cites Families (15)

• 2014
  • 2014-07-16 CN CN201480041182.5A patent/CN105408511B/zh active Active
  • 2014-07-16 WO PCT/JP2014/003767 patent/WO2015015735A1/ja active Application Filing
  • 2014-07-16 KR KR1020157036796A patent/KR101809812B1/ko active IP Right Grant
  • 2014-07-16 MY MYPI2016700273A patent/MY160981A/en unknown
  • 2014-07-16 JP JP2014553008A patent/JP5700182B1/ja active Active
  • 2014-07-16 US US14/908,176 patent/US20160168673A1/en not_active Abandoned
  • 2014-07-28 TW TW103125665A patent/TWI526547B/zh not_active IP Right Cessation

Also Published As

Similar Documents

Legal Events